1. Field Of The Invention
The present invention relates to a procedure and an apparatus for transmitting binary messages in a serial communication bus, several transmitting stations being connected to said bus. More specifically, the procedure is one in which each station is able to transmit a message when the bus is free, and in which, in a signal collision situation when several stations attempt to transmit messages simultaneously, each station monitors the message which is passing through the bus and only the station which has the highest priority is allowed to go ahead and transmit its message while each station having a lower priority which, when transmitting a signal of a logic state assigned a recessive status, receives a signal of a logic state assigned a dominating status cancels its transmission attempt.
2. Description Of Related Prior Art
The multimaster serial bus is based on the idea that each station is allowed to start a transmission any time when the bus is free. Therefore, collisions occur in the bus when two or more stations start transmission simultaneously. Using the bit arbitration method, a signal collision in a multimaster bus can be managed in such manner that the message of the highest priority is transmitted while the other stations wait until said high-priority message has been passed through. This is implemented by assigning one of the logic states a recessive status and the other a dominant status. The so-called AMI (Alternative Mark Inversion) code meets the requirement that a dominant bit has precedence over a recessive bit. In AMI coding, every second dominating bit is transmitted with a different polarity and a recessive bit is equivalent to a free bus. The first bit of each message is transmitted with a different polarity from that of the previous message. This means that it is necessary to know which way the bus connection leads are to be mounted to allow control of the collision.